EVIDENCE AGAINST A ROLE FOR HUMAN T-CELL LYMPHOTROPHIC VIRUS TYPE-I (HTLV-I) IN THE PATHOGENESIS OF AMERICAN CUTANEOUS T-CELL LYMPHOMA

We used a standard polymerase chain reaction (PCR)/Southern blot assay (sensitivity >10(-5)) to detect human T-cell lymphotrophic virus type I (HTLV-I) proviral pX, pol, and env genes in the lesional skin of 42 American patients with cutaneous T-cell lymphoma (CTCL), As in some p rior reports using similar methods, a variable proportion of PCR tests were positive (seven of 42 for pX, three of 42 for pol, and two of 37 for env), resulting in an overall positive test rate of 12 of 121 (10 %). To determine the significance of these positive test results, we p erformed several additional studies, D1S80 polymorphism analysis of CT CL cases and HTLV-I PCR analysis of non-CTCL dermatosis controls showe d no evidence that positive PCR tests resulted from sample mislabeling , gross HTLV-I contamination, or human endogenous retroviruses. We the n modified the standard Ce assay to incorporate ultraviolet (UV) light to destroy low-level PCR contamination. With this modified assay (sen sitivity >10(-5)), only three of 12 previously positive cases were sti ll positive, suggesting that the earlier positives were due to trace c ontamination of PCR reagents or trace contamination of sample DNA, Thi s interpretation was also supported by: (i) a match between pX and pol sequences cloned from one PCR-positive specimen and the MT4-positive control, (ii) our inability to confirm HTLV-I in any PCR-positive case using genomic dot blotting (sensitivity > 10(-2)), and (iii) negative PCR results when new samples from two of the remaining positive cases were analyzed, Finally, we used our modified UV/PCR/Southern blot ass ay to test an additional 28 cases of American CTCL for pX, All of them were negative, Although these studies of 70 cases of American CTCL do not exclude the possibility that another virus is involved in the pat hogenesis of this disease, they provide strong evidence against a role for HTLV-I. Furthermore, they emphasize the need for special strategi es to control for false-positive PCR tests that can result from even t race levels of contamination with viral DNA, As a consequence, associa tions between diseases and viruses should be viewed skeptically if the y are based primarily on conventional PCR data.